(Horticulture) Pheromone of Apple Sawfly: New Tool for Management of a Re-emerging Pest

Apple sawfly, Hoplocampa testudinea, is a damaging pest of commercial apple trees. Adults emerge from the soil in spring and mate. Females are attracted to apple blossoms and lay eggs. Once the larvae hatch, they feed along the surface of young fruits causing ribbon-like scars which downgrade fruit. If the larvae enter the fruit, they tunnel in 3-4 fruits per apple cluster creating a sticky brown frass, making fruits drop or be unmarketable.

In unsprayed or organic orchards apple sawfly can cause up to 90% crop loss; even at lower damage levels the costs of sorting the unmarketable fruit are a loss to the grower. Organic growers have no effective means for controlling apple sawfly other than removing infested shoots which is highly labour-intensive and still results in yield loss. In conventional orchards, apple sawfly has previously been controlled using broad-spectrum insecticides against other pests. The majority of these have now been withdrawn and apple sawfly is re-emerging as a problem even in sprayed orchards. Furthermore, spraying during flowering is to be avoided as this may impact pollinating insects and disrupt integrated pest and disease management programmes used by growers.

Female sawflies attract males using long-range sex pheromones. If the chemical structures of the components of the sex pheromone of apple sawfly could be identified and synthesised, these could be used to help reduce the damage caused by this pest. Traps baited with the pheromone can be used to detect the presence of apple sawfly and apply control methods more efficiently. The pheromone might also be used to control apple sawfly by approaches such as mass trapping and mating disruption. These approaches have been used against other insect pests where the pheromone has been identified. The pheromones are non-toxic natural products, specific for the target pest and without effect on other animals and plants, and they are active in very small amounts.

The project partners have previously attempted to identify the sex pheromone of apple sawfly, but have been unsuccessful due to difficulties in obtaining sufficient live insects for the work. Apple sawfly has only one generation per year and there are no known methods for laboratory culture. This short project will bring together academic and commercial partners in a concerted attempt to overcome this constraint.

The knowledge and facilities of the grower partners will be used to locate orchards previously infested with apple sawfly. The academic and commercial partners will work together to develop methods for isolation of larvae and pupae from the soil and then will collect and process larger soil samples. The larvae and pupae will be reared through to adults and the process of pheromone identification will be started. It is unlikely that this will be fully completed within this project, but the results will provide a firm basis for identification of the pheromone and development of its use for management of apple sawfly in future projects. The opportunity will also be taken to set up a network of traps for monitoring adult sawfly and assess the damage caused, providing new data on the distribution and phenology of this pest.

Academic partners in this project are the Natural Resources Institute, University of Greenwich, which has over 50 years of experience in identification and application of insect pheromones, and NIAB East Malling, the leading UK fruit research institute. Commercial partners are Russell IPM who already produce and sell more than 150 insect pheromones, Avalon Ltd and Agrovista, two agronomy groups who regularly advise UK growers on pest control, and Mole End and Rudford Farms, two organic apple growers who experience significant apple sawfly damage. We also have support from Delphy and PCFruit, leading fruit research and development organisations in The Netherlands and Belgium, respectively, which are keen to find new solutions to managing apple sawfly.

Apple sawfly, Hoplocampa testudinea, is a damaging pest of commercial apple trees. In unsprayed or organic orchards it can cause up to 90% crop loss. In conventional orchards, it has previously been controlled using broad-spectrum insecticides against other pests. Withdrawal of these is leading to re-emergence of apple sawfly as a serious pest.

Identification of the female sex pheromone of apple sawfly could provide the basis for development of new approaches to monitoring and control of this pest. The project partners have previously attempted to identify the pheromone, but have been unsuccessful due to difficulties in obtaining sufficient live insects for the work. Apple sawfly has only one generation per year and there are no known methods for laboratory culture. This short project will bring together academic and commercial partners in a concerted attempt to overcome this constraint.

At least five orchards previously infested with apple sawfly will be located. The academic and commercial partners will work together to optimise methods for isolation of larvae and pupae from the soil by sieving and/or flotation, and then collect and process larger soil samples. Larvae and pupae will be reared through to adults at NIAB and the process of pheromone identification will be started at NRI. It is unlikely that this will be fully completed within this project, but the results will provide a firm basis for identification of the pheromone and development of its use for management of apple sawfly in future projects. In addition, a network of traps for monitoring adult sawfly will be set up and damage assessed, providing new data on the distribution and phenology of this pest.

Academic partners are the Natural Resources Institute of the University of Greenwich and NIAB East Malling. Commercial partners are biocontrol company, Russell IPM, two agronomy groups, Avalon Ltd and Agrovista, and two organic apple growers, Mole End and Rudford Farm.